Professor Stephen Faulkner

Research

Our interests lie in designing and making systems with interesting photophysical properties, which can be used for assay in drug discovery and diagnosis in vitro and in vivo. Our main interests centre on the synthesis and use of metal complexes as imaging and contrast agents, and on the coordination chemistry and electronic structure of the actinide elements involved in the nuclear fuel cycle.

Research within the Faulkner group centres on five themes:

Defining a new chemical toolkit through an understanding of the behaviour of labile species in solution and enabling chemical scientists to use the whole of the periodic table to address medical problems.

Understanding where the molecule ends; and thus establishing the role of weak interactions and solvent structure in determining the properties of molecular and biological systems.

Developing smart spectroscopic and imaging techniques that can be used on scales from the molecule to man, and developing appropriate probe molecules.

Controlling and exploiting self-assembly of therapeutic and diagnostic agents in vivo; and using such systems to optimize transport of such agents to target sites and obviate the possibility of excretion occurring more quickly than localization at the target.

Synthetic Chemistry

We are focused on preparing metal complexes from kinetically stable building blocks, and developing new methods that can be used for linking building blocks together Cyclen provides an ideal scaffold from which to hang pendent arms bearing donor atoms, giving rise to a range of hosts which bind irreversibly to lanthanide ions and which can be used as building blocks to assemble more complicated arrays The example shown on the left shows how two macrocycles can be linked together through a phenolic chromophore before complexation to yield a bimetallic lanthanide complex. Further synthetic elaboration can be used to control the colour of the complex (in this case through diazotisation) and the ability of the phenoxide to act as a donor to the metal ions (in this case through the incorporation of an electron withdrawing group).

Alternatively, building blocks can be linked together to form polymetallic complexes, either through the formation of covalent bonds; for instance, in the synthetic scheme shown to the right, reaction of a complex bearing a pendent amine with the dianhydride of DTPA gives rise to a molecule with three metal binding sites, only two of which are occupied. Since the original complex is kinetically stable, there is no migration of the bound lanthanide ions into the third binding site. Further reaction can be used to form a heterotrimetallic complex. This kind of approach represents the first effective method of carrying out controlled synthesis of heterometallic lanthanide complexes and underpins our development of f-f' and d-f hybrids as single molecule multi-modal imaging agents.

We are also developing methods by which stable complexes can be linked to "targeting vectors" (i.e. molecular fragments that direct a drug or imaging agent to a specific receptor or cell). For instance the Ugi reaction is particularly effective for such purposes, since it allows four components to be combined in a single reaction.

Imaging and Spectrosopy

We have spent many years studying the luminescence from metal complexes, and are particularly interested in the way in which energy is transferred from a sensitiser to the emissive state, and in the way in which transient spectroscopy can be used to probe and rationalise reactivity.

We have developed techniques for time-gated imaging and lifetime mapping, allowing us to image very low concentrations of imaging agent, and allow parallel processing (i.e., the simultaneous detection of a variety of probes). Long-lived luminescence can be separated from background signals by time-gating, allowing very low concentrations of probe complexes to be detected(<10-15M). The figure to the right shows how a time-gated image can be used to distinguish between long-lived lanthanide luminescence (still visible in the image) and short-lived background fluorescence.

Targeting vector conjugates can also be used in imaging. The tetrapeptide tuftsin (ThrLysProArg) is specifically internalised by activated macrophages, and tuftsin conjugates with Gd3+ complexes can be used as MRI contrast agents to image inflammation. Polymetallic complexes incorporating a component which has long lived luminescence as well as one or more gadolinium ions for MRI can be used for imaging by both techniques, circumventing problems with differences in biodisctribution between luminescent and MRI probes.